<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="../../s/vue/2.7.16/vue.min.js"></script>
</head>
<body>

	<div id="example">
		<div>{{value.sequence}}</div>
		<button @click="add">ADD</button>
	</div>
	<script>
		new Vue({
			el : '#example',
			data : {
				value : {
					sequence : 1
				}
			},
			watch : {
				'value.sequence' : function(newVal, oldVal) {
					console.log(oldVal + '->' + newVal);
				}
			},
			methods : {
				add : function() {
					this.value.sequence += 1;
				}
			}
		});
	</script>

</body>
</html>